Apple TV will be getting an untethered jailbreak very soon. Developers at ATV3 Chip Group have an exact date for you and it`s February 1st 2013. The software will be free and will obviously add extra functionality to the Apple TV.
"Engineers are performing the final tests on the jailbreak to determine whether the program is compatible with the beta version or not. Visitors, who can’t wait until the beginning of February, can download the tethered version of the jailbreak. However, users won’t be able to reboot their Apple TV 3 without a PC connection, which is why the untethered version is the most recommended."
"The production of the jailbreaking software has been very long because the ATV3 Dev Team wanted to make sure their program really works. There have been many fake jailbreaks released on the Internet, so Dev Team wants to deliver customers the high quality product they have been looking for."